The dynamic aspects of sound--the amplitude and frequency changes that occur over time--are crucial for auditory perception and communication. The ability of the auditory system to follow and to resolve such changes is the topic of this proposal. More specifically, the proposed project is a comprehensive behavioral study, using normal-hearing adults, of the ability to extract information from changes in the amplitude and the spectrum of sound. The proposal consists of three related projects that investigate increasingly complex aspects of dynamic auditory processing. The first project addresses basic issues of intensity coding and is generally concerned with how normal human hearing can operate over a huge intensity range (120 dB). The proposed experiments address hypotheses that are relevant to this dynamic range problem and examine the role of such processes as suppression, cochlear efferents, middle ear muscles, and nonlinear spread of excitation. The second project examines the ability of the auditory system to extract information from dynamic changes in the amplitude and frequency produced by modulation (AM and FM). The general aim of this project is to develop a comprehensive account of AM and FM processing, including delineation of those aspects of the amplitude envelope that are important for detection and discrimination. The third project is concerned with supra-threshold amplitude processing and, as such, represents a significant extension of previous research. The hypotheses driving the specific research questions are based upon theory and data from threshold phenomenon. The general aim of this project is to extend our understanding of dynamic processing to more realistic auditory stimuli. Overall, these projects will provide information of fundamental importance for understanding certain basic properties of normal human hearing and, eventually, for understanding the consequences of hearing impairment. Of particular importance from the standpoint of health, is the proposed work on intensity coding--dynamic range limitation is perhaps the most important consequence of cochlear loss. Also, the work on supra-threshold processing should lead directly to an understanding of the effects of loudness recruitment, another potential important consequence of cochlear impairment.